As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of such a package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is produced by folding and sealing a web of laminated packaging material. The packaging material has a multilayer structure comprising a layer of fibrous material, e.g. paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene; and, in the case of aseptic packages for long-storage products, such as UHT milk, the packaging material comprises a layer of oxygen-barrier material, e.g. aluminium foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material eventually forming the inner face of the package contacting the food product.
Such packages are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material. The web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, after sterilization, is removed, e.g. vaporized by heating, from the surfaces of the packaging material; and the web of packaging material so sterilized is maintained in a closed sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form the finished, e.g. substantially parallelepiped-shaped packages.
Alternatively, the packaging material may be cut into blanks, which are folded on forming spindles to form the packages, which are then filled with the food product and sealed. An example of this type of package is the “gable-top” package commonly known by the trade name Tetra Rex (registered trademark).
To open the above packages, various solutions have been proposed, one of which, known from U.S. Pat. No. 4,655,387 and No. 4,410,128, consists in forming, at a corner of a flap on the package, a preferential tear line defined by a succession of perforations extending through the outer layers of the packaging material down to the barrier material layer; and the package is opened by lifting the flap and cutting or tearing along the perforations. Needless to say, packages of this sort, once opened, cannot be closed again, and must therefore be handled with care to avoid spillage of the food product until the package is emptied.
To overcome this drawback, packages of the above type are fitted with closable opening devices, which substantially comprise a frame defining an opening and applied about a hole or a removable or pierceable portion in a wall of the package; and a cap hinged to the frame. The cap is normally molded integrally with the frame, and is initially sealed to the frame, along a peripheral edge surrounding the opening, by a thin breakable annular connecting portion. Once unsealed, the cap is movable between a closed position cooperating hermetically with the frame, and an open position. Alternatively, threaded caps separate from and initially screwed to the frame are also used.
One problem of opening devices of the type described is that the cap must be detachable from the frame with practically no effort required when unsealing the package. For which purpose, the opening devices are made of low-break-strength plastic material, normally polyethylene.
Polyethylene, however, has the drawback of failing to act as an effective oxygen barrier. On the side of the packaging material eventually defining the inside of the package, therefore, the hole is closed by an additional patch comprising a small sheet of heat-seal plastic material, and the opposite side of the packaging material is fitted with an oxygen barrier element, e.g. a pull-off tab, which is heat sealed to the patch and has a layer of aluminium.
Providing the packages with a patch and barrier element, however, calls for additional processing of the packaging material before it is sterilized and folded and sealed to form the vertical tube, so that the packages take longer, and hence are more expensive, to produce.
Moreover, once the cap is opened, access to the content of the package also involves removing the barrier element.
Closable opening devices have therefore been proposed by which the package can be opened in one operation, while at the same time ensuring an effective oxygen barrier.
In the solution described in International Patent Application WO 95/05996, such opening devices substantially comprise a frame having a cylindrical collar defining a pour opening and fitted about a pierceable portion of the package; a removable cap which is screwed externally to the frame collar to close the opening; and a substantially tubular cutting member screwed inside the frame collar and having an end edge with a number of substantially triangular end teeth, which cooperate with the pierceable portion of the package to detach it partly, i.e. with the exception of a small peripheral portion, from the relative wall.
The cutting member is operated by the cap via one-way ratchet-type transmission means activated when removing the cap from the collar, and spirals with respect to the frame from a raised rest position in which the end teeth face the pierceable portion, to successive lowered cutting positions in which the end teeth interact simultaneously with the pierceable portion.
A drawback of opening devices of the above type is that the cut part of the pierceable portion tends, in use, to at least partly clog the open section of the cutting member, and therefore the pour opening, thus interfering with outflow of the product from the package.
Moreover, for functional reasons, the cutting member is normally made of material (e.g. polypropylene) structurally more rigid than that of the frame and cap (normally polyethylene), thus possibility resulting in excessive fragility of the end teeth of the cutting member, which may snap off during transport and/or when unsealing the package, and so become dispersed in the food product.
These problems have been solved by the solution described in EP-A-1 088 765, wherein the end edge of the cutting member comprises a single cutting edge acting along a predominant peripheral portion of the pierceable portion of the package.
In addition to cutting, a single cutting edge moving spirally and acting along a predominant peripheral portion of the pierceable portion of the package also exerts thrust on the cut part of the pierceable portion, and tends to fold it inwards of the package and outwards of and eventually around the cutting member, thus preventing the cut part of the pierceable portion from interfering with outflow of the product from the package.
Moreover, using an appropriately designed single cutting edge enables a high degree of efficiency of the cutting member, which may therefore be made of less rigid material, e.g. the same as the cap and frame, and may advantageously be molded in one piece with the frame.
Though usable to advantage in most applications, the above solution is limited as regards the material from which the pierceable portion of the package is made. That is, when the pierceable portion is made of particularly tough material, such as a barrier material covered with a polymer catalyzed by means of an organometal or metallocene, the latter tends to “stretch” rather than tear under the action of the cutting edge, thus forming threadlike residue on the cutting edge, which may get into the food product.